1. Field of the Invention
The invention relates to a disk brake with mechanical self-boosting which is intended in particular for motor vehicles.
2. Description of the Prior Art
Hydraulically actuated disk brakes without self-boosting, which are currently conventional, have a brake bracket and a caliper. The brake bracket and the caliper are parts resting one inside the other; the brake bracket is mounted fixedly on one steering knuckle or the like of a vehicle and retains the caliper transversely displaceable to a brake disk by means of a caliper guide. As their actuating unit, hydraulic disk brakes have a piston-cylinder unit, in which the cylinder is usually part of the caliper. With the piston, a friction brake lining can be pressed against one side of the brake disk. A reaction force displaces the caliper transversely to the brake disk, and as a result the caliper presses a second friction brake lining against the other side of the brake disk and brakes it. Because of the transverse displaceability, the caliper of such disk brakes is known as a floating caliper. In the circumferential direction, or more precisely parallel to a circumferential direction of the brake disk, the friction brake linings are braced on the brake bracket; as a result, a frictional or braking force exerted upon braking by the rotating brake disk on the friction brake linings pressed against the brake disk is transmitted directly to the brake bracket and not to the brake bracket via the caliper and the caliper guide. Because of this construction, the caliper guide is largely free of forces; the braking and frictional forces are transmitted from the friction brake linings to the brake bracket, and the actuating and contact-pressure force of the friction brake linings against the brake disk are internal forces of the caliper.
The situation is different in disk brakes with mechanical self-boosting. They have a self-boosting mechanism, for instance with a ramp mechanism or wedge mechanism. In other words, a friction brake lining is displaceable in the circumferential direction of the brake disk and is braced on a ramp or the like mounted in the caliper. The ramp is a support face extending obliquely at an angle to the brake disk and it need not necessarily be flat and instead can also have a curved course. If for actuation of the disk brake the friction brake lining is pressed against the brake disk, the rotating brake disk, because of the friction existing between it and the friction brake lining, presses the friction brake lining in the circumferential direction. As a result of the bracing of the friction brake lining on the ramp extending obliquely to the brake disk, a wedge effect is obtained, which exerts an additional contact-pressure force of the friction brake lining against the brake disk. The aforementioned contact-pressure force of the friction brake lining against the brake disk is greater than an actuating force that the actuating unit exerts on the friction brake lining. Examples of such disk brakes with mechanical self-boosting by means of a ramp mechanism are found in German Patent Disclosure DE-OS 20 52 496, German Patent DE 198 19 564 C2, and German Patent Disclosure DE 100 37 055 A1; the last two of these references disclose disk brakes that are actuated electromechanically, and the first of these references discloses a disk brake actuated via cables and levers.
A frictional force exerted, when the disk brake is actuated, in the circumferential direction on the friction brake lining by the rotating brake disk is introduced into the caliper via the ramp, and it must be transmitted from the caliper guide to the brake bracket or some other fixed component. This force acts transversely to the caliper guide. The caliper guide must be dimensioned so as to be adequately stable for transmitting the frictional force exerted by the rotating brake disk on the friction brake lining. At the same time, the force to be transmitted from the caliper guide upon braking impairs smooth running of the caliper guide.
The above remarks apply accordingly for other self-boosting mechanisms, such as a lever mechanism, in which a lever that is oblique to the brake disk braces the friction brake lining that is pressed against the brake disk. The lever mechanism can in theory be considered as analogous to the ramp mechanism.